Lead poisoning in the United States is a serious health problem which is estimated to affect some 3 to 4 million children under the age of six years old. To prevent this number from growing, the federal government has mandated that all properties subsidized by the Department of Housing and Urban Development (HUD) must be inspected by the year 1995. This means that approximately 2,000,000 properties must be inspected over the next 5 years. To accomplish this task, a measurement protocol must be established which is not only accurate and reliable, but also very fast. The most modern and practical approach to this problem is to use on-site quantitative screening by X-ray fluorescence (XRF) analysis. Several such systems are currently on the market for this purpose, but in a recent HUD sponsored study, none of these systems performed well in making field-based measurements. The investigator proposes to develop a new, portable XRF system which can accurately and reliably measure low levels of lead in painted structures. Using our new system, home inspectors will be able to measure lead levels as low as 0.5mg/cm2 with a statistical accuracy of 0.05mg/cm2. Furthermore, our system will be able to perform such a measurement in about 10 seconds. By integrating our concept with modern microprocessor based electronics and a rugged ergonomic design, the entire screening process will be made much more efficient and accurate.